1. Technical Field
The present disclosure relates to systems and methods for targeting and analyzing an area of a process-free plate, e.g., for reading dot coverage and/or rendering an image of the targeted area of the plate on a display.
2. Background Art
Modern lithographic printing plates have a photosensitive top layer applied to a substrate, typically aluminum. Part of the photosensitive layer is exposed to light, and either the exposed or unexposed portion of this layer is removed. The traditional lithographic workflow removes the exposed (or unexposed) portion of the photosensitive layer as part of a developing process that is performed before mounting the plate on a printing press. Quality control measurements of the plate using imaging techniques can be taken before mounting the plate, and the contrast between the remaining photosensitive layer and the revealed substrate enables routine computation of the dot coverage. Measuring dot coverage may comprise, for example, measuring the size, spacing or angle of the dots that make up a printed image.
Printing plates known as process-free plates do not have a developing process applied to them before they are mounted on a press (see, e.g., U.S. Pat. No. 4,115,127 to Ikeda, et al.). Note that for the purposes of the present disclosure, the term “process-free plates” is intended to encompass any “low-contrast” plate, including but not limited to “processless,” “latent image” or “semi-latent image” plates. Such process-free plates exhibit limited contrast between the photosensitive layer and the substrate. The contrast is generally on the same order as the variation in reflected intensity within each homogeneous region of exposed or unexposed photosensitive material. As a result, traditional methods for targeting and analyzing printing plates, e.g., measuring dot coverage, are often ineffective with respect to process-free plates.
Although the variation in intensity within the homogeneous regions is due to properties of the plate itself, and not due to noise introduced by the imaging system of a measurement device, enhancement of the image to enable computing the dot coverage of process-free plates may still be viewed as an image de-noising problem. Numerous techniques have been developed for image de-noising (see, e.g, U.S. Pat. Nos. 7,120,308, 7,260,269 and 7,352,90 to Guleryuz; PCT Publication No. WO/2006/050364A to Awate et al.; and Buades, B. Coll, J. M Morel, “A review of image de-noising algorithms, with a new one,” Multiscale Modeling and Simulation (SIAM interdisciplinary journal), Vol 4 (2), pp: 490-530, 2005).
There are a number of types of dot patterns used to produce the different density levels on a plate image. Of note, most types of dot patterns try to avoid both high frequency and low frequency components.
Despite efforts to date, there is a need for improved systems and methods for targeting, measuring and/or otherwise analyzing process-free plates. These and other needs are satisfied by the systems and methods of the present disclosure.